This invention relates to remedial wellbore cementing operations.
The general procedure of drilling an oil or gas well includes drilling a borehole using a drilling fluid. Subsequent to drilling the borehole, casing is run into the well preparatory to placing a cement in the annulus between the outside of the casing and the borehole wall. A good seal is not easy to obtain, however. When a poor cementing job results, it may be necessary to cut or perforate the casing and squeeze cement under high pressure through the cut or perforations into the annulus and try to fill the zones that were not properly cemented initially. Even this may not be successful and can result in eventual abandonment of the hole. For instance, if the cement is allowing unavoidable fluid flow through channels which are smaller than about 1/1000 of an inch, squeeze cementing is not feasible even with microfine ground cement, yet this is exactly what frequently happens; channels such as cracks or worm holes having a dimension of about 5/10,000-inch to 8/10,000-inch result during the cementing or develop over time from the effect of salt water or acidizing. Even when conventional squeeze cementing is feasible, it frequently requires milling cuts into the casing which is more expensive than simply perforating.
Polymers are broadly known for use in oilfield drilling and production operations. Clarke, U.S. Pat. No. 4,897,119 (Jan. 30, 1990) discloses using a small amount of a low molecular weight polymer as a dispersant for blast furnace slag in a cement slurry.
Novak, U.S. Pat. No. 4,547,298 (Oct. 15, 1985) and Novak, U.S. Pat. No. 4,760,882 (Aug. 2, 1988), disclose primary cementing using a drilling fluid containing a polymeric material which is hardened with a chemical initiator and, optionally, radiation. Perry et al, U.S. Pat. No. 3,114,419 (Dec. 17, 1963) discloses radiation copolymerization in a wellbore of an alkylidene bisacrylamide and an ethylenic monomer as an improvement over chemical polymerization initiators.
Ionomers are known polymeric compositions which have been available since the 1950's. In recent years they have found a utility in applications such as tooth fillings as described, for instance, in Japanese patent 85-144069/24 (04.05.85).